1. Field of the Invention
This invention relates to a display control apparatus having a function of superimposing graphics data and text data upon each other on a display.
2. Description of the Related Art
There is a known technique of superimposing a character, i.e., text data, upon a graphics image, i.e., graphics data, on a display apparatus such as a CRT or a FPD (Flat Panel Display).
In such a technique, in general, each character to be displayed is stored in a text memory in the form of a character code and attribute data indicative of display colors (colors of the character and the back ground), while each graphics image is stored in a graphics memory in the form of graphics data designating the color of each display pixel. Text data for designating the color of each display pixel on a display screen is generated from the character code and attribute data, and one of the text data and graphics data is selected and supplied to the display device, thereby obtaining a synthesized image.
In the conventional display control apparatus, however, the text data can be superimposed upon the graphics data only when the bit numbers (widths) of the both data items are equal to each other. For example, graphics data of 8 bits (256 colors can be designated) cannot be superimposed upon text data of 4 bits (16 colors can be designated). Therefore, where graphics data is superimposed upon text data of 4 bits, more than 16 colors cannot be used for displaying a graphics image, though 256 colors can be used at most if only the graphics data is used.